%0 Journal Article
%T A HIFI preview of warm molecular gas around χ Cygni: first detection of H2O emission toward an S-type AGB star
%A Justtanont, K.
%A Decin, L.
%A Schöier, F. L.
%A Maercker, M.
%A Olofsson, H.
%A Bujarrabal, V.
%A Marston, A. P.
%A Teyssier, D.
%A Alcolea, J.
%A Cernicharo, J.
%A Dominik, C.
%A de Koter, A.
%A Melnick, G.
%A Menten, K.
%A Neufeld, D.
%A Planesas, P.
%A Schmidt, M.
%A Szczerba, R.
%A Waters, R.
%A de Graauw, Th
%A Whyborn, N.
%A Finn, T.
%A Helmich, F.
%A Siebertz, O.
%A Schmülling, F.
%A Ossenkopf, V.
%A Lai, R.
%J Astron. Astrophys.
%D 2010
%V 521
%F Justtanont_etal2010
%O exported from refbase (https://db.rplab.ru/refbase/show.php?record=1096), last updated on Fri, 17 Jun 2016 17:12:56 -0500
%X Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg.Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been performed to derive the temperature, density, and velocity structure of the circumstellar envelope.Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters for the circumstellar envelope, we modelled both the ortho- and para-H2O lines. Our modelling results are consistent with the velocity structure expected for a dust-driven wind. The derived total H2O abundance (relative to H2) is (1.1±0.2) × 10-5, much lower than that in O-rich stars. The derived ortho-to-para ratio of 2.1±0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere.
%K HEB mixer applications
%K HIFI
%K Herschel
%K stars: AGB and post-AGB / circumstellar matter / stars: kinematics and dynamics / stars: individual: χ Cyg / stars: late-type / stars: mass-loss
%R 10.1051/0004-6361/201015092
%U https://doi.org/10.1051/0004-6361/201015092
%P L6